The present invention relates to deformable articles particularly to extensibly deformable articles and to methods for assessing the degree of deformation of such articles visually.
For many deformable articles, for example extensible articles it is desirable to be able to assess when a pre-determined degree of extension has been achieved. For example it may be desirable to know when a particular material has been extended to a value which is close to its elastic limit in order to avoid exceeding said limit. Such methods are useful in many areas where either an article""s extension or the compression or tension it transfers to another object must be known, and where instrumentation is impractical.
In the field of medicine, extensible fabrics are often used in dressings and bandages and if these are applied too tightly to a patient, problems may result due to the high pressure applied. In extreme cases blood flow can be severely impaired and damage to body tissues can result.
For example compression bandages are used primarily in the treatment of leg ulcers where venous insufficiency is a major factor. The compressive forces promote good valve performance in the veins leading to more efficient blood circulation and thus better healing.
However the main perceived difficulty for users of compression bandages is ensuring that enough pressure is applied to a limb to achieve therapeutic benefit without over-tightening the bandage. This often results in under tightening thus greatly reducing any therapeutic benefits.
It is known that figures on the surface of a bandage may act as an indication of the amount of tension. Such a device is disclosed in U.S. Pat. No. 3,613,679.
U.S. Pat. No. 4,133,307 discloses a device where the elastic strip runs within a non-extensible, partly transparent tube where both the strip and tube have markers which when aligned give an indication of the amount of tension.
There is thus a need to provide an effective and convenient way of determining when an extensible article has been extended to a particular degree.
Therefore in accordance with the present invention there is provided an extension indicator comprising first and second cooperating members, each being adapted to be secured to an extensibly deformable article, in which one of said members is more extensible than the other and in which each member bears visual indication means which upon extension of the more extensible member are adapted to align with each other to indicate a predetermined extension of the more extensible member.
The invention further provides an article comprising an extensible material and including an extension indicator in accordance with the invention and as herein described.
By xe2x80x98extensiblexe2x80x99 is meant the ability of the member to be stretched without breaking.
According to a first embodiment of the invention there is provided an extension indicator including at least a first member comprising a transparent extensible layer with a first image present and a second member comprising a layer with a second image present and where the first layer overlays the second layer and the first layer can extend independently relative to the second layer.
Transparency is defined as being able to see through easily and distinctly. Transparency may be achieved by using a transparent material or by cutting slits or holes into an opaque material.
The first and second layers may be connected in such a way that the connection does not impede relative extension of the layers. For example the first layer and the second layer may be connected along a line perpendicular to the axis of extension. Alternatively the first and second layer may be independently bonded to a substrate with no direct connection between layers.
For use as an extension indicator as hereinbefore described the first layer is allowed to extend with respect to the second layer. The images visible on or through the layers change position with relative extension between the layers to indicate extension. On reaching the correct extension the images come into a recognizable alignment, for example the images overlap to give a single image or a single image is positioned between two images.
In one aspect of this first embodiment of the present invention there is provided an extension indicator comprising at least a first transparent extensible layer with a first image present and a second layer with a second image present and a third extendible layer where the first and third layer encapsulate the second layer, and the first layer can extend independently relative to the second layer.
The indicator is aptly at least 0.1 cm long and may be at least 5 cm long (when measured along the length of the indicator prior to the stretching of the fabric). Stretching of the article to a pre-determined extent may cause the indicator to extend for example by at least 10, 50, 100 or 200% for example.
According to a second embodiment of the present invention there is provided an extension indicator comprising at least a first layer wherein the layer contains a slit in the direction of extension, markings on opposite sides and adjacent to the slit and a region of variable elasticity on at least one side of the slit.
For use as an extension indicator as hereinbefore described the indicator is extended and due to the region of variable elasticity on at least one side of the slit, the markings on each side move relative to each other. The correct extension is indicated when the markings line up in a predetermined manner.
Elasticity is the extent to which a material stretches under a given tension.
The extension indicator may comprise at least a first layer where the layer contains a slit in the direction of extension, markings on opposite sides and adjacent to the slit and a region of variable elasticity on at least one side of the slit.
Alternatively the extension indicator may be part of an extensible article in that the article contains a slit in the direction of extension and at least two markings on opposite sides and adjacent to the slit and a region of variable elasticity on at least one side of the slit.
According to a third embodiment of the present invention there is provided an extension indicator comprising at least a first member, for example a layer of material overlaying a second member, for example a second layer of a material wherein the first layer includes an extensible shape with a perforation and the second layer includes an image bearing surface.
For use as an extension indicator in this embodiment of the invention the first layer and the second layer with an image bearing surface are allowed to extend with respect to each other. The image visible through the perforation in the first layer changes with relative extension between the layers to indicate extension. This is achieved by the first layer having a different elasticity to the second layer.
Preferably the first layer has a modulus of elasticity that varies along its length. This can be achieved by having a first layer with a non-uniform shape, for example, a triangle. If a triangle is anchored only at its ends, an applied tension that stretches the triangle will extend the triangle more at the thin end (a single vertex) than at the thick end (a double vertex). Thus when the triangle is fixed to an image bearing surface and the surface is extended, there will be relative movement between the triangle and the surface, thus changing the image visible through a perforation, for example a hole in the triangle.
Preferably the extension indicator comprises a first layer comprising a triangular piece of fabric with a perforation at one end fixed to an image bearing surface. Extension is to be indicated along a longitudinal axis of the image bearing surface. The triangle is fixed to the surface along one edge on a lateral axis, with the perforation in a corner at a point furthest from the fixed edge. The comer is also fixed to the surface. The image bearing surface is provided with markings, the relative position of which to the perforation indicate whether the correct extension has been achieved.
In one aspect of this embodiment a single mark may be provided which coincides with the perforation on the correct extension. In another aspect at least two marks may be provided on each side of where the perforation coincides with the single mark on the correct extension. In this example, when the marks are not visible the correct extension has been achieved.
In accordance with a fourth embodiment of the present invention there is provided an extension indicator for an extensible article wherein said first and second members comprise first and second substantially overlapping strips, each strip being provided with first and second ends, and wherein
(i) the first end of the first strip is attached to the extensible article,
(ii) the second end of the second strip is attached to the extensible articles
(iii) the first strip is substantially transparent and has a first image on it, and the second strip has a second image on it, and,
(iv) the second end of the first strip and the first end of the second strip substantially overlap.
For use as an extension indicator as hereinbefore described the two strips are allowed to move with respect to each other. The images visible through the strips change position with relative movement between the strips to indicate extension of the extensible article. On reaching the correct extension the images come into a recognizable alignment, for example the images overlap to give a single image or a single image is positioned between two images.
In order to protect the indicator, the indicator may be provided with an extensible, substantially transparent top layer which may or may not be attached to the indicator.
Furthermore to aid application of the indicator to an article the indicator may be attached to an extensible base layer.
In one aspect of this fourth embodiment of the present invention there is provided an extension indicator for an extensible article comprising at least a first and second substantially overlapping strip, each with a first and second end where
(i) the first end of the first strip is attached between an extensible base layer and an extensible, substantially transparent top layer.,
(ii) the second end of the second strip is attached between the extensible base layer and the extensible, substantially transparent top layer,
(iii) the first strip is substantially transparent and has a first image on it and the second strip has a second image on it,
(iv) the second end of the first strip and the first end of the second strip substantially overlap, and
(v) the extensible base layer is attached to the extensible article.
Desirably the indicator does not substantially impede stretching of the extensible article, ie. the force required to stretch an article to a given degree is not substantially increased by the presence of the indicator.
One or more indicators may be placed at different positions on the article in order to assess the extension at different regions of the article. For example, if indicators are placed at different positions along the length of an extensible article the indicators may indicate the same degree of extension if it desired for the article to be stretched to the same degree along its length or they may indicate different degrees of extension if it is desired for the article to be stretched to the different degrees along its length to provide graduated extension.
The indicator preferably contrasts in color and/or design with the article in order that it can be clearly seen.
Extension indicators in accordance with the invention have many applications but are especially useful in the areas of compression therapy in which the extensible article is an extensible bandage. Such bandages may be used in a method for the treatment of one or more of the following disorders; namely; venous disorders, lymphodoema, which comprises applying a bandage or article according to the invention to the affected site on a patient.
Apart from uses in the medical area the extension indicators of the present invention have applications in other areas such as replacements for conventional force sensors, pressure sense extension indicators, strain indicators and dynamic decorations. A wide range of applications include weigh scales, barometers, exercise equipment, sports equipment, toys, packaging and clothing.
As a weigh scale, the material of the extension indicator is preferably elastic and could provide the spring force directly, providing a light, flexible, collapsible weighing device. An object could be weighed by holding one end of the indicator and fastening the object to the other end. The extension of the indicator could then be calibrated to read directly the weight of the object. This has the advantage of being easy to pack and carry, for example for walking, fishing and hunting.
In another example, the indicator could be fastened in-line with an object to which tension is being applied, and calibrated to display the tension. The large scale, easy-to-read indication would be an advantage in, for example, tensioning sails, tensioning guy ropes for tents or other structures, tensioning bows for archery, or tensioning strings on musical instruments.
In a further example, the indicator is attached across an object, the extension of which is to be indicated. As the indicator is light in weight and conformable, it is particularly suited as an indicator to show correct inflation of inflatable objects such as footballs, boats, or tires. Similarly, the indicator could be used to show how a material is stretched over an object. For example, if attached to the extendible clothing, it could be used to give a direct visual read-out of a person""s measurements. In this application, the conformability and the softness of the indicator are major advantages, along with light weight and ease of reading. Another advantage is that the extension indication is positioned directly on the surface of the object concerned, so the user does not have to look away to a separate gauge.
In the case where the extensible article is a bandage the indicator may be located centrally or along an edge of a article. If more than one indicator is provided these may be located together or separately to enhance visibility on application of the article, for example in bandage form, to a patient.